1. Field of the Invention
This invention relates to inflatable automotive vehicle safety restraint devices such as air bags, side air curtains or the like. More particularly, the invention relates to a process that combines sewing and thermoplastic fusion of knitted, woven and non-woven coated textile fabric in the manufacture of these safety devices. When the coated textile fabric is sewn and heat sealed in the process, a portion of the coating material flows into the stitch holes and seals them, thus providing a strong, airtight air bag structure. The process also provides a means for an improved, more efficient and semi-continuous manufacturing process for stitching and sealing the air bags and side air curtains.
2. Description of the Related Art
Present safety restraint devices for automotive vehicles include driver and passenger side air bags that are rapidly inflated by a gasxe2x80x94sometimes referred to herein as xe2x80x9cairxe2x80x9dxe2x80x94which is produced by explosion of a pyrotechnic material at the time of a collision. The devices provide a protective barrier between the vehicle occupants and the vehicle structure. Much of the impact of a collision is absorbed by the air bag, thus preventing or, in many cases, lessening the possibility of serious bodily injury to the vehicle occupants. Air bags are typically stored in a collapsed, folded condition in the steering wheel to protect the driver, and in the dashboard to protect a front seat passenger., The automotive industry has recently introduced side air bags that are stored in the back of the front seats or in the rear seats to protect the cabin occupants in the event of a collision occurring on either side of the vehicle. More recently still, a further safety feature that has been made available for passenger vehicles, especially the so-called sport utility vehicles (SUVs), and minivans, is the side-impact protective inflatable side air curtain that is designed to provide a cushioning effect in the event of side collisions or rollover accidents. These side air curtains are stored uninflated along the roof of the vehicle or in one of the main support pillars of the vehicle. In the event of a collision the side air curtain deploys along the interior side walls of the vehicle cabin, protecting the occupants from serious bodily injury from contact with the vehicle structure and from broken glass.
Each of these various types of air bags has different design and physical property requirements, such as gas (air) holding permeability, air pressure and volume, and puncture resistance. For example, driver and front passenger air bags, which inflate and deflate almost immediately thereafter, must have little or no permeability; passenger side air bags require a controlled permeability. Side air curtains, on the other hand, must retain air pressure for relatively longer periods of time than other types of air bags. Moreover, all vehicle air restraint devices must have superior packageability and anti-blocking properties. Packageability refers to the ability of a relatively large device such as an air bag to be packed in a relatively small space, such as within a steering wheel or within a vehicle support pillar. Anti-blocking properties refers to the ability of the device to deploy instantaneously when needed without any resistance caused by the material sticking to itself, particularly after being stored for relatively long periods of time. These and other physical properties are determined in large part by the type of fabric and weave used in the air bag, whether the fabric is knitted, woven or non-woven, and, importantly, the nature of the coatings that are used on the fabric.
The air holding capability of side air curtains is critical since they must remain inflated for extended periods of time to protect passengers in multiple rollover accidents. Unlike air bags, which are designed to inflate instantaneously and to deflate almost immediately after inflation to avoid injury to the driver and front seat passenger, side air curtains used in SUVs, or in ordinary passenger vehicles must be capable of remaining inflated from about 3 to about 12 seconds depending upon the size of the air curtain and the size and type of vehicle involved. An average passenger vehicle would require a side air curtain of from about 60 inches to about 120 inches in length measured along the side of the vehicle. A larger vehicle, such as a minivan, would require an even longer side air curtain. The inflation period of a side air curtain should be sufficient to protect the cabin occupants during at least three rollovers, the maximum usually experienced in such. incidents.
When side air curtains are deployed they may be subjected to extreme pressures within a relatively broad range depending upon their specific location or application. For example, air bag deployment pressures are generally in the range of from about 50 kilopascals (kpa) to about 450 kpa, which corresponds generally to a range of from about 7.4 psi (pounds per square inch) to about 66.2 psi. Since sewing or stitching is used in the manufacture of the air bag structure, air can easily escape at these pressures through the stitch holes unless the stitches are sealed or fused by RF welding or other types of sealing.
Accordingly, there is a need for fabric products and methods of construction for air bags that will be relatively impermeable to fluids under such anticipated pressures while also being relatively light in weight.
One means of improving air holding capability in vehicle restraint devices has been through coatings such as chloroprene and silicone rubber coatings applied to a textile (e.g., nylon) fabric. U.S. Pat. No. 5,110,666 discloses a woven nylon fabric coated with polyurethane to provide the desired permeability and retention of inflation gas. Nevertheless, wherever coated fabrics are used the problems of controlling air permeability, air pressure, and volume remain. Insufficiency of adhesion of the coating material to the textile fabric substrate also is a serious problem that must be addressed. For example, the smoother the textile fabric surface generally the more difficult it is to obtain strong adhesion of the coating material to the fabric. With some coatings such as silicone rubber (polysiloxane), radio frequency (RF) heat sealing techniques cannot be used to form the air bag because this material will not flow at heat sealing temperatures. In such instances, air bags are usually made by stitching, a process that requires the addition of an adhesive sealant in the stitched areas. Even so, leakage of air occurs at the stitching, which lessens the protective capability of the air bag.
U.S. Pat. No. 5,863,644 discloses woven or laid structures using hybrid yams comprising reinforcing filaments comprised of thermoplastic polymers to form textile sheet materials of adjustable gas and/or liquid permeability. During the formation of textile fabrics in accordance with the disclosure, polyester fibers in the weaves are melted by the application of heat to form textile sheet materials that are stated to have predetermined gas and/or liquid permeability.
Improved polyurethane, acrylic, polyamide, and silicone coatings that are coated in layers on the fabrics have recently been developed. It has been found that adhesion and heat sealing characteristics are greatly improved with such layered coatings. Examples of such coated fabrics and methods of coating such fabrics are disclosed in copending commonly assigned applications Ser. Nos. 09/327,243, filed Jun. 7, 1999, now U.S. Pat. No. 6,239,046 B1, 09/327,244, filed Jun. 7, 1999, abandoned in favor of 09/956,639, filed Sep. 19, 2001, and 09/327,245 filed Jun. 7, 1999, abandoned in favor of 09/956,640, filed Sep. 19, 2001, the disclosures of which are incorporated herein by reference and made a part of this disclosure. Another example of a greatly improved bonding system is a polyurethane epoxy resin and polysiloxane beaded heat seal, that is disclosed in copending commonly assigned application Ser. No. 09/452,030, filed Nov. 30, 1999, now U.S. Pat. No. 6,350,709 B1, which is incorporated herein by reference and made a part of this disclosure. A further development in air bag technology is disclosed in another commonly assigned copending application Ser. No. 09/459,768, filed Dec. 13, 1999, now abandoned, in which the inflatable safety device incorporates connective tubular tethers within the restraint device to provide structural support and stiffening when it is inflated. This application is also incorporated herein by reference and made a part of this disclosure. My copending provisional application Ser. No. 60/178,897, filed Jan. 28, 2000 relates to a Sewn Fusion Seal Process for producing air-holding vehicle restraint systems as disclosed herein. The disclosure of my provisional application Ser. No. 60/178,897 is also incorporated herein by reference.
Despite the advances made in air bag coating technology, problems inherent in controlling air permeability, pressure and volume remain. One such problem involves air loss resulting from the fact that during the manufacture of the air bags coated textiles are stitched together by sewing. Each stitch creates a potential leak that adversely affects the integrity and air-holding capability of the bag. At present, stitched or sewn areas of air bag construction are sprayed with an acrylic, polyurethane, polyurethane acrylic, polymeric, or other type of synthetic resin to be made airtight. The present invention addresses this problem and presents a method for stitching and thermoplastically fusing the stitched seam that results in a strong, sealed air bag structure that has superior air-holding ability and that can be adapted, if desired, for incorporation in a semi-continuous process for the manufacture of air bags.
It has been found that by using a combination of sewing and thermoplastic fusion in the manufacture of air bags (collectively including air bags, side air bags and side air curtains), the leakage of air through stitch holes is eliminated or so substantially reduced as to be negligible in effect. This process results in an inflatable air-holding automotive vehicle restraint system that is able to withstand the explosive pressures of inflation and is adaptable for use in a semi-continuous manufacturing process.
A method is disclosed for producing an air-holding vehicle restraint system, comprising coating a textile fabric on at least one side with a thermoplastic polymeric material, folding the coated textile fabric along its lengthwise direction to form a closed bottom end and two open upper ends, with the coated side of the fabric facing inwardly, and folding a portion of each of the upper open ends of the textile fabric so that they turn outwardly to form a coated platform. The method further comprises laying a sealing tape upon said coated platform, securing one sealing tape to the coated platform, sealing the sealing tape to said coated platform, cutting the coated textile fabric along predetermined side edges to form an air-holding vehicle restraint system of desired shape, and sealing the cut side edges of the coated textile fabric. Preferably, the sealing tape is secured to the coated platform by sewing. The step of sealing the sealing tape to the coated platform preferably is accomplished by heat. Further, the side edges of the textile fabric are sealed by sewing and heat sealing. The method further comprises the step of folding the upper open ends of the taped, sealed platform upwardly and securing them together form a tubeshaped structure at the upper end of the air-holding vehicle restraint system. The step of securing the upper ends together is accomplished preferably by sewing. Other securing means are contemplated. Alternatively, the method may include the step of coating the second side of the textile fabric.
The textile fabric is preferably comprised of synthetic fibers which are selected from the group consisting of polyamides and polyesters. Preferably the textile fabric is a knitted, woven, or non-woven fabric, and is preferably woven nylon.
Preferably, the coating of thermoplastic polymeric material on the at least one side of the textile fabric comprises a first adhesive coating layer selected from the group consisting of aromatic or aliphatic polyester or polyether polyurethanes and a second elastomeric coating layer which comprises an elastomeric polyether or polyester polyurethane. The sealing tape comprises a textile fabric coated on at least one side with a thermoplastic polymeric material and the polymeric material coating on the sealing tape is preferably polyurethane
The first mentioned textile fabric is comprised of synthetic fibers and the textile fabric is a knitted, woven, or non-woven fabric. The textile fabric of the sealing tape is comprised of synthetic fibers and is knitted, woven, or non-woven, and the synthetic fibers thereof are selected from the group consisting of polyamides and polyesters. The textile fabric of the sealing tape is woven nylon.
According to the method the sealing tape is laid upon the coated platform with its thermoplastic polyurethane coating in face-to-face contacting relationship with said polyurethane coated platform. The adhesive coating layer has a coating weight of from about 0.3 ounces/sq. yd. to about 1.5 ounces/sq. yd. and the second coating layer has a solids content of from about 30% to about 100% by weight. The second coating layer has a coating weight of from about 1 ounce/sq.yd. to about 8 ounces/sq.yd. The coating of thermoplastic polymeric material comprises a first adhesive layer selected from the group consisting of aromatic or aliphatic polyester or polyether polyurethanes and a second elastomeric coating layer consisting of an elastomeric polyether or polyester polyurethane.
According to an alternative embodiment, an additional intermediate layer is positioned between the coated platform and the coated sealing tape. The intermediate layer comprises an electroconductive strip of unsupported film. The unsupported electroconductive film strip is sewn between said coated platform and the coated sealing tape and has electroconductive material therein. The electroconductive material is selected from the group consisting of powdered metal, carbon black, stainless steel and aluminum, and is in the form of particles interspersed therethrough. The unsupported electroconductive strip is preferably a polyurethane film. The heat sealing step is effected by radio frequency sealing, preferably from about 10 to about 80 megahertz. Hot air sealing or ultrasonic sealing are also contemplated.
An air-holding vehicle restraint system is disclosed which comprises a textile fabric having a thermoplastic polymeric coating on at least one side thereof, the coated fabric being folded along its lengthwise direction to form a closed bottom end and two open upper ends, with the coated side of the fabric facing inwardly, each of the upper open ends of the textile fabric being turned outwardly to form a coated platform. A sealing tape is positioned upon the coated platform and in contact therewith, and means is provided to secure the sealing tape to the coated platform. The sealing tape is sealed to the coated platform and said coated textile fabric is cut along predetermined side edges. Means is provided to seal the cut side edges of the coated textile fabric to form an air-holding vehicle restraint system of desired shape. Alternatively, the second side of the textile fabric may be coated with a polymeric material.
According to an alternative embodiment, an intermediate layer is positioned between the coated platform and the coated sealing tape. The intermediate layer comprises a conductive unsupported film strip, preferably polyurethane, having interspersed therethrough, conductive material such as powdered metal, carbon black, stainless steel, aluminum or the like. The conductive strip facilitates heat sealing in a microwave oven by generating heat through the microwave action.